This is the last article in the 650b vs 700c trilogy. First was all about the maximum comfort so I tested everything on a fully equipped bike (Lauf Grit SL fork, suspension seatpost and suspension stem). Then it was all about a rigid bike without any comfort improving parts. The last part is focusing on one, but very supple Soma Cazadero tire in three different variants that I tested them on a very interesting Canyon Grail bike. Now, I am ready to tell you if you should jump into the 650b bandwagon!
The first article ended without any conclusive result because when you use something like Lauf Grit SL fork, suspension stem and suspension seastpost, the tire/wheel combo is somehow less important and the results between different wheels/tire size are very close. So it was all about your personal preference: smaller wheels and more nimble/agile handling or bigger wheels and better rolling characteristics (riding on bigger bumps but also maintaining speed on the road). The second article where I was comparing only the front end using a rigid bike was much more informative. This time we learned that indeed, the smaller but wider 650b wheel/tire combination was significantly improving the comfort but those results were based on rather stiff Panaracer Gravelking SK tires. So naturally, I wanted to find out what will change (if anything) when I will make the 650b vs 700c comparison based on a very supple Soma Cazadero tire. Finally, I was able to do exactly that! I got a 700x50c Cazadero, a 700x42c one and a 650b 50mm variant.
This time I also changed the benchmark bike and used the opportunity to test those tires on Canyon Grail bike. It is considered to be a rather stiff bike when riding on tops so it was a good bike to make the objective comparisons. I only measured front end vibrations at the hoods (I did not have second 700x50c tire but also not that many bikes can accommodate that big tire at the rear) but to make sure that rear of the bike is not influencing the results in any significant way, the rear tire (700x40c Schwalbe G-One bite) was run at 25 PSI and I also used a Redshift Suspension seatpost that made my body bounce much less on any road imperfections. So it was all about the front end vibrations.
Based on my previous experience, I set the correct air pressure based on this formula: (narrower tire width divided by a wider tire width) * (air pressure of the narrower tire). The starting point was 700x42c tire that I usually run at 25 PSI. So 700x50c tire was run at 21 PSI and 650b 50mm at 21,5 PSI (because it has only slightly less air that 700c 50 mm variant). With 700c tires, I used the carbon DT Swiss GRC 1400 Spline wheels and for 650b tires, I used an alloy WTB Asym i23 TCS 650b. Both wheels have rather big inner width (24 mm and 23 mm respectively) so the tires could be inflated to properly wide shapes. But to my surprise, none of the 50 mm variants were really 50 mm wide (it was more about 47 mm in both cases). 42 mm was 42mm on a carbon DT Swiss rim. In every case, the tires were set up tubeless to be sure that the inner tube is not influencing the results in any way.
For those who follow my site for some time, there will be no surprise in the fact that the right tire is crucial for riding comfort. The more supple the tire the better the overall comfort. My test shows that a good supple tire makes the differences between 650b and 700c wheels much less noticeable. When you compare the results you see a quite steady decrease in vibration between bigger and smaller volume but it is not as significant as you would expect (especially on a bumpy forest route you gain only about 3-4% less vibration when switching from 700x42c to 650bx50 tire). The biggest improvement is when switching from 700x42c to 700x50c but again it is still less than 8%. On a fast gravel route with high-frequency chatter, the difference is a little more visible but again it is only 8% fewer vibration when comparing 650b 50 mm to 700x42c tire. And the difference between 650b 50mm and 700x50c tire is almost negligible (2,6%) although subjectively a bigger wheels roll much better than smaller 650b one. Subjectively is the keyword here because it comes down to your feelings. For me, 650b wheels/tires are less enjoyable than 700x42c and the small difference in comfort (when using a supple tire) is not enough incentive for me to switch to 650b wheels. Especially, when using something like Redshift suspension stem and suspension seatpost that improves the comfort to the point that you simply will have a hard time noticing any differences between smaller and bigger tire (in terms of compliance).
So, there you have it!
I am staying with 700c wheels and 40ish tires because in my opinion, when used with a properly supple tire, this is the best possible combination of rolling characteristics and overall comfort. Of course, you can always say, that 650b has much more potential in terms of comfort because there are more and more bikes that can take even 60 mm 650b tire but let’s be honest here. To make it really useful, you would have to run that wide tire at something like 18 PSI which in my opinion (and based on my tests with Schwalbe ThunderBurt 2,25 inch tire) compromises the handling too much and because of that, I am not anymore in the bandwagon of wider and wider 650b tires. But I am also not in the 700x50c bandwagon because again, I believe that the added comfort comes at the big price of compromised handling. Something like 700c 40-45mm supple tire is the way to go because in that setup you get the best of two worlds: best comfort and great handling.